Light emitting device with improved current spreading performance and lighting apparatus including the same

ABSTRACT

Disclosed herein is a light emitting device exhibiting improved current spreading. The disclosed light emitting device includes a light emitting structure including a first conductivity type semiconductor layer, a second conductivity type semiconductor layer, and an active layer disposed between the first conductivity type and second conductivity type semiconductor layers, a first electrode disposed on the first conductivity type semiconductor layer, and a second electrode disposed on the second conductivity type semiconductor layer. The light emitting structure includes a mesa etching region where the second conductivity type semiconductor layer, active layer, and first conductivity type semiconductor layer are partially etched, thereby exposing a portion of the first conductivity type semiconductor layer. The first electrode is disposed on the exposed portion of the first conductivity type semiconductor layer. A first electrode layer is disposed between the second conductivity type semiconductor layer and the second electrode. A second electrode layer is disposed between portions of the first electrode layer spaced from each other at opposite sides of the mesa etching region.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of co-pending U.S. patent applicationSer. No. 14/308,101 filed on Jun. 18, 2014, which claims priority under35 U.S.C. §119 to Korean Application No. 10-2013-0070104, filed in Koreaon Jun. 19, 2013, which is hereby incorporated in its entirety byreference as if fully set forth herein.

TECHNICAL FIELD

Embodiments relate to a light emitting device and a lighting apparatusincluding the same.

BACKGROUND

Light emitting devices, such as light emitting diodes (LEDs) and laserdiodes, which use a Group III-V or Group II-VI compound semiconductormaterial, may render various colors such as red, green, blue, andultraviolet by virtue of development of thin film growth technologiesand device materials. It may also be possible to produce white light athigh efficiency using fluorescent materials or through color mixing.Further, the light emitting devices have advantages, such as low powerconsumption, semi-permanent lifespan, fast response time, safety, andenvironmental friendliness as compared to conventional light sources,such as fluorescent lamps and incandescent lamps.

Therefore, these light emitting devices are increasingly applied totransmission modules of optical communication units, light emittingdiode backlights as a replacement for cold cathode fluorescent lamps(CCFLs) constituting backlights of liquid crystal display (LCD) devices,and lighting apparatuses using white light emitting diodes as areplacement for fluorescent lamps or incandescent lamps, headlights forvehicles and traffic lights.

FIG. 1 is a cross-sectional view of a conventional light emittingdevice. FIG. 2 is a top image view illustrating current spreading of thelight emitting device in FIG. 1. FIG. 1 illustrates a cross-sectionalview taken along line A-A of FIG. 2.

Referring to FIG. 1, the conventional light emitting device, which isdesignated by reference numeral “1”, includes a substrate 10, and alight emitting structure 20 disposed on the substrate 10. The lightemitting structure 20 includes a first conductivity type semiconductorlayer 22, an active layer 24, and a second conductivity typesemiconductor layer 26. The light emitting structure 20 has a mesaetching region M where portions of the second conductivity typesemiconductor layer 26, active layer 24, and first conductivity typesemiconductor layer 22 are removed through etching.

A first electrode 30 is disposed on a portion of the first conductivitytype semiconductor layer 22 exposed through the etching region M. Asecond electrode 40 is disposed on an unetched portion of the secondconductivity type semiconductor layer 26. A transparent electrode layeris disposed between the second conductivity type semiconductor layer 26and the second electrode 40.

However, the conventional light emitting device 1 may have a followingproblem.

Referring to FIG. 2, current from the second conductivity typesemiconductor layer 26 flows while bypassing the mesa etching region Mbecause the transparent electrode layer 50 is not present in the mesaetching region M. As a result, current spreading is ineffective and, assuch, there may be a phenomenon in which current is concentrated aroundthe second electrode 40.

SUMMARY

Embodiments provide a light emitting device exhibiting improved currentspreading and a lighting apparatus including the same.

In an embodiment, a light emitting device includes a light emittingstructure including a first conductivity type semiconductor layer, asecond conductivity type semiconductor layer, and an active layerdisposed between the first conductivity type semiconductor layer and thesecond conductivity type semiconductor layer, a first electrode disposedon the first conductivity type semiconductor layer, and a secondelectrode disposed on the second conductivity type semiconductor layer,wherein the light emitting structure includes a mesa etching regionwhere the second conductivity type semiconductor layer, the activelayer, and the first conductivity type semiconductor layer are partiallyetched, thereby exposing a portion of the first conductivity typesemiconductor layer, and the first electrode is disposed on the exposedportion of the first conductivity type semiconductor layer in the mesaetching region, wherein a first electrode layer is disposed between thesecond conductivity type semiconductor layer and the second electrode,and a second electrode layer is disposed between portions of the firstelectrode layer spaced from each other at opposite sides of the mesaetching region.

Each of the first electrode layer and the second electrode layer may bea transparent electrode layer.

The second electrode layer may overlap, at opposite ends thereof, thefirst electrode layer.

The second electrode layer may overlap a portion of the mesa etchingregion.

The first electrode may be disposed beneath the second electrode layer.

An insulating layer may be disposed between the mesa etching region andthe second electrode layer.

The insulating layer may be disposed inside a portion of the lightemitting structure exposed through the mesa etching region.

An empty space may be present between the second electrode layer and thefirst electrode.

The insulating layer may fill the space between the second electrodelayer and the first electrode.

The second electrode layer may contact the first electrode layer, andmay have a higher level than the first electrode layer at a locationwhere the second electrode layer contacts the first electrode layer.

The second electrode layer may be thicker than the first electrodelayer.

The insulating layer may enclose the first electrode.

In another embodiment, a light emitting device includes a light emittingstructure including a first conductivity type semiconductor layer, asecond conductivity type semiconductor layer, and an active layerdisposed between the first conductivity type semiconductor layer and thesecond conductivity type semiconductor layer, a first electrode disposedon the first conductivity type semiconductor layer, and a secondelectrode disposed on the second conductivity type semiconductor layer,wherein the light emitting structure includes a mesa etching regionwhere the second conductivity type semiconductor layer, the activelayer, and the first conductivity type semiconductor layer are partiallyetched, thereby exposing a portion of the first conductivity typesemiconductor layer, and the first electrode is disposed on the exposedportion of the first conductivity type semiconductor layer in the mesaetching region, wherein a first electrode layer is disposed between thesecond conductivity type semiconductor layer and the second electrode,and a plurality of second electrode layer units is disposed betweenportions of the first electrode layer spaced from each other at oppositesides of the mesa etching region.

Each of the first electrode layer and the second electrode layer may bea transparent electrode layer. Adjacent ones of the second electrodelayer units may have a non-uniform spacing.

The spacing between the second electrode layer units may be graduallyreduced in a direction from a pad portion of the second electrode to anend portion of the second electrode.

The second electrode layer units may be gradually increased in number ina direction from a pad portion of the second electrode to an end portionof the second electrode.

The second electrode units may have non-uniform widths, respectively.The widths of the second electrode layer units may be graduallyincreased in a direction from a pad portion of the second electrode toan end portion of the second electrode.

An insulating layer may be disposed between the mesa etching region andthe second electrode layer.

The insulating layer may be disposed inside a portion of the lightemitting structure exposed through the mesa etching region.

The insulating layer may fill a space between the second electrode layerand the first electrode.

In another embodiment, a lighting apparatus includes a light sourcemodule including the light emitting device according to one of theabove-described embodiments, a reflection plate disposed on a bottomcover, a light guide plate disposed on the reflection plate, and anoptical sheet disposed on the light guide plate.

BRIEF DESCRIPTION OF THE DRAWINGS

Arrangements and embodiments may be described in detail with referenceto the following drawings in which like reference numerals refer to likeelements and wherein:

FIG. 1 is a cross-sectional view of a conventional light emittingdevice;

FIG. 2 is a top image view illustrating current spreading of the lightemitting device in FIG. 1;

FIG. 3 is a cross-sectional view of a light emitting device according toa first embodiment;

FIG. 4 is a plan view of the light emitting device according to thefirst embodiment;

FIG. 5 is a plan view of a light emitting device according to a secondembodiment;

FIG. 6 is a plan view of a light emitting device according to a thirdembodiment;

FIG. 7 is a plan view of a light emitting device according to a fourthembodiment;

FIG. 8 is a cross-sectional view of a light emitting device according toa fifth embodiment;

FIG. 9 is a view illustrating a light emitting device package accordingto an embodiment including one of the light emitting devices accordingto the above-described embodiments;

FIG. 10 is a view illustrating a head lamp according to an embodiment,in which a light emitting device or light emitting device packageaccording to one of the above-described embodiments is disposed; and

FIG. 11 is a view illustrating a lighting system according to anembodiment in which light emitting device packages according to theabove-described embodiment are disposed.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Hereinafter, embodiments will be described with reference to the annexeddrawings.

It will be understood that when an element is referred to as being “on”or “under” another element, it can be directly on/under the element, andone or more intervening elements may also be present. When an element isreferred to as being “on” or “under”, “under the element” as well as “onthe element” can be included based on the element.

In the drawings, the thickness or size of each layer is exaggerated,omitted, or schematically illustrated for convenience of description andclarity. In addition, the size or area of each constituent element doesnot entirely reflect the actual size thereof.

FIG. 3 is a cross-sectional view of a light emitting device according toa first embodiment. FIG. 4 is a plan view of the light emitting deviceaccording to the first embodiment. FIG. 3 illustrates a cross-sectionalview taken along line B-B of FIG. 4.

Referring to FIGS. 3 and 4, the light emitting device according to thefirst embodiment, which is designated by reference numeral “100A”, mayinclude a substrate 110, and a light emitting structure 120 disposed onthe substrate 110.

The light emitting device 100A includes a light emitting diode (LED)using a plurality of compound semiconductor layers, for example,semiconductor layers of Group III-V or Group II-VI elements. The LED maybe a colored LED to emit blue, green, or red light, a white LED, or anultraviolet (UV) LED. Light emitted from the LED may be diversifiedthrough variation of kinds and concentrations of materials constitutingthe semiconductor layers, although the present disclosure is not limitedthereto.

The light emitting structure 120 includes a first conductivity typesemiconductor layer 122, an active layer 124, and a second conductivitytype semiconductor layer 126.

The light emitting structure 120 may be formed using, for example, metalorganic chemical vapor deposition (MOCVD), chemical vapor deposition(CVD), plasma-enhanced chemical vapor deposition (PECVD), molecular beamepitaxy (MBE), hydride vapor phase epitaxy (HVPE), or the like. Ofcourse, the formation method is not limited to the above-describedmethods.

The first conductivity type semiconductor layer 122 may be made of asemiconductor compound, for example, a Group III-V or Group II-VIcompound semiconductor. The first conductivity type semiconductor layer122 may be doped with a first conductivity type dopant. When the firstconductivity type semiconductor layer 122 is an n-type semiconductorlayer, the first conductivity type dopant is an n-type dopant. Then-type dopant may include Si, Ge, Sn, Se, Te, or the like, although thepresent disclosure is not limited thereto. When the first conductivitytype semiconductor layer 122 is a p-type semiconductor layer, the firstconductivity type dopant is a p-type dopant. The p-type dopant mayinclude Mg, Zn, Ca, Sr, Ba, or the like, although the present disclosureis not limited thereto.

The first conductivity type semiconductor layer 122 may include asemiconductor material having a formula of Al_(x)In_(y)Ga_(1-x-y)N(0≦x≦1, 0≦y≦1, and 0≦x+y≦1). The first conductivity type semiconductorlayer 122 may include at least one element of Ga, N, In, Al, As, and P.The first conductivity type semiconductor layer 122 may be made of atleast one of GaN, InN, AlN, InGaN, AlGaN, InAlGaN, AlInN, AlGaAs,InGaAs, AlInGaAs, GaP, AlGaP, InGaP, AlInGaP, and InP.

The second conductivity type semiconductor layer 126 may be made of asemiconductor compound, for example, a Group III-V or Group II-VIcompound semiconductor. The second conductivity type semiconductor layer126 may be doped with a second conductivity type dopant. When the secondconductivity type semiconductor layer 126 is a p-type semiconductorlayer, the second conductivity type dopant is a p-type dopant. Thep-type dopant may include Mg, Zn, Ca, Sr, Ba, or the like, although thepresent disclosure is not limited thereto. When the second conductivitytype semiconductor layer 126 is an n-type semiconductor layer, thesecond conductivity type dopant is an n-type dopant. The n-type dopantmay include Si, Ge, Sn, Se, Te, or the like, although the presentdisclosure is not limited thereto.

The second conductivity type semiconductor layer 126 may include asemiconductor material having a formula of Al_(x)In_(y)Ga_(1-x-y)N(0≦x≦1, 0y≦1, 0≦x+y≦1). The second conductivity type semiconductor layer126 may include at least one element of Ga, N, In, Al, As, and P. Thesecond conductivity type semiconductor layer 126 may be made of at leastone of GaN, InN, AlN, InGaN, AlGaN, InAlGaN, AlInN, AlGaAs, InGaAs,AlInGaAs, GaP, AlGaP, InGaP, AlInGaP, and InP.

The following description will be given in conjunction with an examplein which the first conductivity type semiconductor layer 122 is ann-type semiconductor layer, and the second conductivity typesemiconductor layer 126 is a p-type semiconductor layer.

Over the second conductivity type semiconductor layer 126, asemiconductor layer having an opposite polarity to the secondconductivity type may be formed. For example, when the secondconductivity type semiconductor layer 126 is a p-type semiconductorlayer, an n-type semiconductor layer (not shown) may be formed over thesecond conductivity type semiconductor layer 126. Thus, the lightemitting structure 120 may be implemented as one of an n-p junctionstructure, a p-n junction structure, an n-p-n junction structure, and ap-n-p junction structure.

The active layer 124 is disposed between the first conductivity typesemiconductor layer 122 and the second conductivity type semiconductorlayer 126.

In the active layer 124, electrons and holes meet and, as such, emitlight with energy determined by the intrinsic energy band of thematerial of the active layer 124 (light emitting layer). When the firstconductivity type semiconductor layer 122 is an n-type semiconductorlayer, and the second conductivity type semiconductor layer 126 is ap-type semiconductor layer, electrons may be injected from the firstconductivity type semiconductor layer 122 into the active layer 124, andholes may be injected from the second conductivity type semiconductorlayer 126 into the active layer 124.

The active layer 124 may have at least one of a single quantum wellstructure, a multi quantum well structure, a quantum wire structure, anda quantum dot structure. For example, the active layer 124 may have amulti quantum well structure through injection of tri-methyl gallium gas(TMGa), ammonia gas (NH₃), nitrogen gas (N₂), and tri-methyl indium gas(TMIn), although the present disclosure is not limited thereto.

When the active layer 124 has a multi quantum well structure, the activelayer 124 may have well and barrier layers having at least one of layerpair structures of InGaN/GaN, InGaN/InGaN, GaN/AlGaN, InAlGaN/GaN,GaAs(InGaAs)/AlGaAs, and GaP(InGaP)/AlGaP, although the presentdisclosure is not limited thereto. The well layer may be made of amaterial having a lower band gap than the barrier layer.

The light emitting structure 120 is supported by the substrate 110disposed beneath the light emitting structure 120.

The substrate 110 may be formed using a material suitable for growth ofa semiconductor material or a material having excellent thermalconductivity. The substrate 110 may be made of at least one of sapphire(Al₂O₃), SiC, GaAs, GaN, ZnO, Si, GaP, InP, Ge, and Ga₂O₃. Wet washingor plasma treatment may be performed upon the substrate 110, to removeimpurities from the surface of the substrate 110.

A buffer layer 112 may be disposed between the light emitting structure120 and the substrate 110. The buffer layer is adapted to reduce latticemismatch and thermal expansion coefficient difference between thematerial of the substrate 110 and the material of the light emittingstructure 120. The buffer layer may be made of a Group III-V or GroupII-VI compound semiconductor, for example, at least one of GaN, InN,AlN, InGaN, AlGaN, InAlGaN, and AlInN.

An undoped semiconductor layer 114 may be disposed between the substrate110 and the first conductivity type semiconductor layer 122. The undopedsemiconductor layer 114 is a layer formed to achieve an enhancement incrystallinity of the first conductivity type semiconductor layer 122.The undoped semiconductor layer 114 may be made of a material identicalto or different from the material of the first semiconductor layer 122.The undoped semiconductor layer 114 exhibits lower electric conductivitythan the first conductivity type semiconductor layer 122 because nofirst conductivity type dopant is doped therein. The undopedsemiconductor layer 114 may be disposed over the buffer layer 112 whilecontacting the first conductivity type semiconductor layer 122. Theundoped semiconductor layer 112 is grown at a temperature higher thanthe growth temperature of the buffer layer 112. The undopedsemiconductor layer 112 exhibits higher crystallinity than the bufferlayer 112.

The light emitting structure 120 includes a mesa etching region M whereportions of the second conductivity type semiconductor layer 126, activelayer 124, and first conductivity type semiconductor layer 122 areremoved through etching. Through the mesa etching region M, the firstconductivity type semiconductor layer 122 is partially exposed.

A first electrode 130 is disposed on the first conductivity typesemiconductor layer 122. A second electrode 140 is disposed on thesecond conductivity type semiconductor layer 126. In detail, the firstelectrode 130 is disposed on the portion of the first conductivity typesemiconductor layer 122 exposed through the mesa etching region M. Thesecond electrode 140 is disposed on an unetched portion of the secondconductivity type semiconductor layer 126.

The first electrode layer 130 may include at least one of Mo, Cr, Ni,Au, Al, Ti, Pt, V, W, Pd, Cu, Rh, and Ir. The first electrode layer 120may be formed to have a single layer structure or a multilayerstructure.

Referring to FIG. 4, the first electrode 130 and second electrode 140may include first and second electrode pad portions 130P and 140P havingrelatively large widths, respectively. The first and second electrodepad portions 130P and 140P may be areas to which wires (not shown) willbe bonded for supply of current to the light emitting device 100A.

An electrode layer 150 is disposed over the light emitting structure120. The electrode layer 150 may be a transparent electrode layer. Theelectrode layer 150 may be disposed over the second conductivity typesemiconductor layer 126 while covering at least a portion of the mesaetching region M.

Since the second conductivity type semiconductor layer 126 may exhibitinferior ohmic characteristics with respect to the second electrode 140,the electrode layer 150 is adapted to improve such electricalcharacteristics. The electrode layer 150 may have a layer structure or amulti pattern structure.

For the electrode layer 150, a transparent conductive layer or a metalmay be selectively used. For example, the electrode layer 150 may bemade of at least one of indium tin oxide (ITO), indium zinc oxide (IZO),indium zinc tin oxide (IZTO), indium aluminum zinc oxide (IAZO), indiumgallium zinc oxide (IGZO), indium gallium tin oxide (IGTO), aluminumzinc oxide (AZO), antimony tin oxide (ATO), gallium zinc oxide (GZO),IZO nitride (IZON), Al—GaZnO (AGZO), In—GaZnO (IGZO), ZnO, IrO_(x),RuO_(x), NiO, RuO_(x)/ITO, Ni/IrO_(x)/Au, Ni/IrO_(x)/Au/ITO, Ag, Ni, Cr,Ti, Al, Rh, Pd, Ir, Sn, In, Ru, Mg, Zn, Pt, Au, and Hf, although thepresent disclosure is not limited thereto.

The electrode layer 150 includes a first electrode layer 151 disposedbetween the second conductivity type semiconductor layer 126 and thesecond electrode 140, and a second electrode layer 152 disposed betweenportions of the first electrode layer 151 spaced from each other atopposite sides of the mesa etching region M.

The first electrode layer 151 is disposed on the unetched portion of thesecond conductivity type semiconductor layer 126. The second electrodelayer 152 is disposed to correspond to the mesa etching region M. Thesecond electrode layer 152 may connect the portions of the firstelectrode layer 151 spaced by the mesa etching region M.

In accordance with an embodiment, a transparent electrode layer may alsobe disposed in the mesa etching region M, not only to uniformly spreadcurrent injected from the second electrode 140 over the light emittingstructure 120, but also to reduce a phenomenon in which current isconcentrated around the second electrode 140. As current is spread up tothe mesa etching region M, an enhancement in light amount of the lightemitting device 100A and an improvement in operating voltage of thelight emitting device 100A may be achieved.

The second electrode layer 152 contacts, at opposite ends thereof, thefirst electrode layer 151. In an embodiment, opposite ends of the secondelectrode layer 152 may overlap the first electrode layer 151. In thiscase, there may be a step at a location where the first electrode layer151 and second electrode layer 152 contact. That is, the secondelectrode layer 152 has a higher level than the first electrode layer151 at the location where the first electrode layer 151 and secondelectrode layer 152 contact.

The second electrode layer 152 may be thicker than the first electrodelayer 151. The second electrode layer 152 is arranged to correspond tothe mesa etching region M, which is a non-emission region, and, as such,there is no possibility of light absorption by the second electrodelayer 152. Accordingly, it may be possible to maximize current spreadingeffects by forming the second electrode layer 152 to be thicker than thefirst electrode layer 151.

Since the second electrode layer 152 is arranged to correspond to themesa etching region M, the first electrode 130 is disposed beneath thesecond electrode layer 152.

The second electrode layer 152 covers at least a portion of the mesaetching region M. The position and size of the second electrode layer152 covering the mesa etching region M may be varied in accordance withembodiments, so long as the second electrode layer 152 connects theportions of the first electrode layer 151 spaced by the mesa etchingregion M. In FIG. 4, the second electrode layer 152 is illustrated asnot being disposed over the first electrode pad portion 130P. Of course,the present disclosure is not limited to the illustrated case. Thesecond electrode layer 152 may be arranged to completely cover the mesaetching region M or to partially cover the mesa etching region M. Thatis, the second electrode layer 152 may overlap a portion of the mesaetching region M.

Referring to FIG. 3, an insulating layer 160 may be disposed beneath thesecond electrode layer 152 in the mesa etching region M. The insulatinglayer 160 may also be disposed on an upper surface of the light emittingstructure 120 in a region where the first electrode layer 151 is notdisposed. The insulating layer 160 may protect side walls of the lightemitting structure 120 exposed through etching while preventingelectrical short circuit between the active layer 124 and the secondelectrode layer 152 or between the first conductivity type semiconductorlayer 122 and the second electrode layer 152. The insulating layer 160may be disposed at the side walls of the light emitting structure 120exposed through mesa etching in the mesa etching region M. Theinsulating layer 160 may function to support the second electrode layer152.

The insulating layer 160 may be made of a non-conductive oxide ornitride. For example, the insulating layer 160 may include a siliconoxide (SiO₂) layer, an oxide nitride layer, or an aluminum oxide layer,although the present disclosure is not limited thereto.

An empty space may be present between the second electrode layer 152 andthe first electrode 130. The second electrode layer 152 may take theform of an air bridge.

FIG. 5 is a plan view of a light emitting device according to a secondembodiment. The cross-sectional view of the light emitting element ofFIG. 5 taken along line B-B of FIG. 5 is identical to FIG. 3 and, assuch, is not again shown and refers to FIG. 3. The content of thisembodiment repeating that of the previous embodiment will be no longerdescribed and, as such, a description will be given only in conjunctionwith the differences of the embodiments.

Referring to FIG. 5, the light emitting device according to the secondembodiment, which is designated by reference numeral “100B”, isdifferent from the light emitting device 100A according to the firstembodiment in that the second electrode layer 152 is disposed in themesa etching region M toward an end portion E of the second electrode140. That is, the mesa etching region M is exposed in a region adjacentto the second electrode pad portion 140P, and the second electrode 152is disposed toward the end portion E of the second electrode 140.

In the conventional light emitting device, a phenomenon in which currentis concentrated occurs because current injected through the secondelectrode 140 flows while bypassing the mesa etching region M and, assuch, smooth flow of current is not exhibited at the end portion E ofthe second electrode 140. In accordance with this embodiment, however,the second electrode layer 152 is disposed in the mesa etching region Mtoward the end portion E of the second electrode 140 and, as such,current may flow through the second electrode layer 152 before bypassingthe mesa etching region M. Accordingly, smooth flow of current may beachieved.

FIG. 6 is a plan view of a light emitting device according to a thirdembodiment. The cross-sectional view of the light emitting element ofFIG. 6 taken along line B-B of FIG. 6 is identical to FIG. 3 and, assuch, is not again shown and refers to FIG. 3. The content of thisembodiment repeating those of the previous embodiments will be no longerdescribed and, as such, a description will be given only in conjunctionwith the differences of the embodiments.

Referring to FIG. 6, in the light emitting device according to the thirdembodiment, which is designated by reference numeral “100C”, the secondelectrode layer 152 may include a plurality of spaced second electrodelayer units 152 a. Although three second electrode layer units 152 a ₁,152 a ₂, and 152 a ₃ are illustrated in FIG. 6, the number of secondelectrode layer units 152 a may be varied in accordance withembodiments.

Adjacent ones of the plural second electrode layer units 152 a may benon-uniform. For example, referring to FIG. 6, the spacing between thesecond electrode layer unit 152 a ₁ disposed at the leftmost and thesecond electrode layer unit 152 a ₂ disposed at the middle, namely, aspacing D₁ differs from the spacing between the second electrode layerunit 152 a ₂ disposed at the middle and the second electrode layer unit152 a ₃ disposed at the rightmost, namely, a spacing D₂.

In accordance with an embodiment, the spacing between the adjacent twosecond electrode layer units 152 a may be gradually reduced in adirection from the pad portion 140P of the second electrode 140 to theend portion E of the second electrode 140 (D₁>D₂). That is, the numberof second electrode layer units 152 a may be gradually increased in themesa etching region M in a direction toward the end portion E of thesecond electrode 140.

In the conventional light emitting device, a phenomenon in which currentis concentrated occurs because current injected through the secondelectrode 140 flows while bypassing the mesa etching region M and, assuch, smooth flow of current is not exhibited at the end portion E ofthe second electrode 140. In accordance with this embodiment, however, aplurality of second electrode layer units 152 a is disposed in the mesaetching region M toward the end portion E of the second electrode 140and, as such, smooth flow of current may be achieved.

FIG. 7 is a plan view of a light emitting device according to a fourthembodiment. The cross-sectional view of the light emitting element ofFIG. 7 taken along line B-B of FIG. 6 is identical to FIG. 3 and, assuch, is not again shown and refers to FIG. 3. The content of thisembodiment repeating those of the previous embodiments will be no longerdescribed and, as such, a description will be given only in conjunctionwith the differences of the embodiments.

Referring to FIG. 7, in the light emitting device according to thefourth embodiment, which is designated by reference numeral “100D”, thesecond electrode layer 152 may include a plurality of spaced secondelectrode layer units 152 a. Although two second electrode layer units152 a ₁ and 152 a ₂ are illustrated in FIG. 7, the number of secondelectrode layer units 152 a may be varied in accordance withembodiments.

The plural second electrode layer units 152 a may have a non-uniformwidth. The width of each second electrode layer unit 152 a means a widthin a direction perpendicular to a longitudinal direction of the mesaetching region M. For example, referring to FIG. 7, the width of thesecond electrode layer unit 152 a ₁ disposed at the left side, namely, awidth W₁ differs from the width of the second electrode layer unit 152 a₂ disposed at the right side, namely, a width W₂.

In accordance with an embodiment, the widths of the plural secondelectrode layer units 152 a may be gradually increased in a directionfrom the pad portion 140P of the second electrode 140 to the end portionE of the second electrode 140 (W₁<W₂).

In the conventional light emitting device, a phenomenon in which currentis concentrated occurs because current injected through the secondelectrode 140 flows while bypassing the mesa etching region M and, assuch, smooth flow of current is not exhibited at the end portion E ofthe second electrode 140. In accordance with this embodiment, however,the widths of the plural second electrode layer units 152 a may begradually increased in a direction toward the end portion E of thesecond electrode 140 and, as such, smooth flow of current may beachieved.

FIG. 8 is a cross-sectional view of a light emitting device according toa fifth embodiment. The content of this embodiment repeating those ofthe previous embodiments will be no longer described and, as such, adescription will be given only in conjunction with the differences ofthe embodiments.

Referring to FIG. 8, in the light emitting device according to the fifthembodiment, which is designated by reference numeral “100E”, aninsulating layer 160 may be disposed in the mesa etching region M. Inaddition, the insulating layer 160 may be disposed between the lightemitting structure 120 and the second electrode layer 152. Theinsulating layer 160 may protect side walls of the light emittingstructure 120 exposed through etching and the first electrode 130 whilepreventing electrical short circuit between the active layer 124 or thefirst conductivity type semiconductor layer 122 and the second electrodelayer 152. The insulating layer 160 may be disposed not only at the sidewalls of the light emitting structure 120 exposed through mesa etching,but also between the second electrode layer 152 and the first electrode130. That is, the insulating layer 160 may be disposed to enclose thefirst electrode 130 beneath the second electrode layer 152.

In the fifth embodiment, the insulating layer 160 may function to morefirmly support the second electrode layer 152 by filling a space betweenthe second electrode layer 152 and the first electrode 130.

The plan view of the light emitting device 100E according to the fifthembodiment may be similar to FIGS. 4 to 7. Variations of the secondelectrode layer 152 described with reference to FIGS. 4 to 7 may also beapplied to the fifth embodiment. No description will be given of suchvariations.

FIG. 9 is a view illustrating a light emitting device package accordingto an embodiment including one of the light emitting devices accordingto the above-described embodiments.

The light emitting device package according to this embodiment, which isdesignated by reference numeral “300”, includes a body 310, first andsecond lead frames 321 and 322 disposed at the body 310, the lightemitting device 100 according to one of the above-described embodiments,which is disposed at the body 300, to be electrically connected to thefirst and second lead frames 321 and 322, and a mold 340 formed in acavity, which may be formed at the body 310. As described above, thelight emitting device 100 has a single chip structure including aplurality of light emitting cells connected in series or in parallel.

The body 310 may be made of a silicon material, a synthetic resinmaterial, or a metal material. When the body 310 is made of a conductivematerial such as a metal material, an insulating layer may be coatedover the surface of the body 310, although not shown, in order to avoidelectrical short circuit between the first and second lead frames 321and 322 and the metal body. Accordingly, it may be possible to avoidelectrical short circuit between the first lead frame 321 and the secondlead frame 322.

The first and second lead frames 321 and 322 are electrically isolatedfrom each other, and supply current to the light emitting device 100.The first and second lead frames 321 and 322 may also reflect lightgenerated from the light emitting device 100 so as to achieve anenhancement in luminous efficacy. In addition, the first and second leadframes 321 and 322 may function to outwardly dissipate heat generatedfrom the light emitting device 100.

The light emitting device 100 may be mounted on the body 310 or on thefirst lead frame 321 or second lead frame 322. In this embodiment, thelight emitting device 100 is directly electrically connected to thefirst lead frame 321 while being connected to the second lead frame 322via a wire 330. The light emitting device 100 may be electricallyconnected to the lead frames 321 and 322, using a flip-chip method or adie-bonding method, in place of the wire-bonding method.

The mold 340 may encapsulate the light emitting device 100, to protectthe light emitting device 100. The mold 340 may include phosphors 350,to change the wavelength of light emitted from the light emitting device100.

The phosphors 350 may include garnet-based phosphors, silicate-basedphosphors, nitride-based phosphors, or oxynitride-based phosphors.

For example, the garnet-based phosphors may be YAG (Y₃Al₅O₁₂:Ce³⁺) orTAG (Tb₃Al₅O₁₂:Ce³⁺). The silicate-based phosphors may be(Sr,Ba,Mg,Ca)₂SiO₄:Eu²⁺. The nitride-based phosphors may beCaAlSiN₃:Eu²⁺ containing SiN. The oxynitride-based phosphors may beSi_(6-x)Al_(x)O_(x)N_(8-x):Eu²⁺ (0<x<6).

Light of a first wavelength range emitted from the light emitting device100 is excited by the phosphors 350 and, as such, is changed into lightof a second wavelength range. As the light of the second wavelengthrange passes through a lens (not shown), the optical path thereof may bechanged.

A plurality of light emitting device packages, each of which has theabove-described structure according to the illustrated embodiment, isprepared, and is then arrayed on a substrate. Optical members, namely,light guide plates, prism sheets, diffusion sheets, etc., may bearranged on optical paths of the light emitting device packages. Suchlight emitting device packages, substrate, and optical members mayfunction as a light unit. In accordance with another embodiment, adisplay apparatus, an indication apparatus or a lighting system may beimplemented using the semiconductor light emitting devices or lightemitting device packages described in conjunction with theabove-described embodiments. The lighting system may include, forexample, a lamp or a street lamp.

Hereinafter, a head lamp, and a backlight unit as embodiments of thelighting system including the above-described light emitting devices orlight emitting device packages will be described.

FIG. 10 is a view illustrating a head lamp according to an embodiment,in which a light emitting device or light emitting device packageaccording to one of the above-described embodiments is disposed.

Referring to FIG. 10, light emitted from a light emitting module 710, inwhich a light emitting device or light emitting device package accordingto one of the above-described embodiments is disposed, passes through alens 740 after being reflected by a reflector 720 and a shade 730, so asto be directed forwardly of a vehicle body.

The light emitting module 710 may include a plurality of light emittingdevices mounted on a circuit board, although the present disclosure isnot limited thereto.

FIG. 11 is a view illustrating a lighting system according to anembodiment in which light emitting device packages according to theabove-described embodiment are disposed.

As shown in FIG. 11, the lighting system according to the illustratedembodiment, which is designated by reference numeral “800”, includes alight source module 830-835, a reflection plate 820 disposed on a bottomcover 810, a light guide plate 840 disposed in front of the reflectionplate 820, to guide light emitted from the light source module 830-835to a front side of the lighting system 800, an optical sheet includingfirst and second prism sheets 850 and 860 disposed in front of the lightguide plate 840, a panel 870 disposed in front of the optical sheet, anda color filter 880 disposed in front of the panel 870.

The light source module 830-835 includes a circuit board 830 and lightemitting device packages 835 mounted on the circuit board 830. Here, aprinted circuit board (PCB) may be used as the circuit board 830. Thelight emitting device packages 835 may have the configuration describedabove in conjunction with FIG. 9.

The bottom cover 810 may receive the constituent elements of thelighting system 800. The reflection plate 820 may be provided as aseparate element, as shown in FIG. 11, or may be formed by coatingmaterial having high reflectivity over a rear surface of the light guideplate 840 or a front surface of the bottom cover 810.

Here, the reflection plate 820 may be made of a material having highreflectivity and capable of being formed into an ultra thin structure.Polyethylene terephthalate (PET) may be used for the reflection plate820.

The light guide plate 840 serves to scatter light emitted from the lightsource module 830-835 so as to uniformly distribute the light throughoutall regions of the lighting system. Therefore, the light guide plate 840may be made of a material having high refractivity and transmissivity.The material of the light guide plate 840 may includepolymethylmethacrylate (PMMA), polycarbonate (PC), polyethylene (PE), orthe like. The light guide plate 840 may be omitted. In this case, an airguide system, which transfers light in a space over the reflective sheet820, may be implemented.

The first prism sheet 850 may be formed by coating a polymer exhibitinglight transmittance and elasticity over one surface of a base film. Thefirst prism sheet 850 may have a prism layer having a plurality ofthree-dimensional structures in the form of a repeated pattern. Here,the pattern may be of a stripe type in which ridges and valleys arerepeated.

The second prism sheet 860 may have a similar structure to the firstprism sheet 850. The second prism sheet 860 may be configured such thatthe orientation direction of ridges and valleys formed on one surface ofthe base film of the second prism sheet 860 is perpendicular to theorientation direction of the ridges and valleys formed on one surface ofthe base film of the first prism sheet 850. Such a configuration servesto uniformly distribute light transmitted from the light source module830-835 and the reflective sheet 820 toward the entire surface of thepanel 870.

In this embodiment, the optical sheet may be constituted by the firstprism sheet 850 and second prism sheet 860. However, the optical sheetmay include other combinations, for example, a microlens array, acombination of a diffusion sheet and a microlens array, and acombination of a prism sheet and a microlens array.

A liquid crystal display panel may be used as the panel 870. Further,instead of the liquid crystal display panel 870, other kinds of displaydevices requiring light sources may be provided.

The display panel 870 is configured such that liquid crystals arelocated between glass bodies, and polarizing plates are mounted on bothglass bodies so as to utilize polarizing properties of light. Here, theliquid crystals have properties between a liquid and a solid. That is,the liquid crystals which are organic molecules having fluidity like theliquid, are regularly oriented, and, as such, display an image usingchange of such molecular orientation due to an external electric field.

The liquid crystal display panel used in the lighting system is of anactive matrix type, and uses transistors as switches to adjust a voltageapplied to each pixel.

The color filter 880 is provided on the front surface of the panel 870,and transmits only a red, green or blue light component of lightprojected from the panel 870 per pixel, thereby displaying an image.

In accordance with the above-described embodiments, current spreading upto the mesa etching region may be achieved and, as such, an enhancementin light amount of the light emitting device and an improvement inoperating voltage of the light emitting device may be achieved.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

What is claimed is:
 1. A light emitting device, comprising: a lightemitting structure comprising a first conductivity type semiconductorlayer, a second conductivity type semiconductor layer, and an activelayer disposed between the first conductivity type semiconductor layerand the second conductivity type semiconductor layer; a first electrodedisposed on the first conductivity type semiconductor layer; and asecond electrode disposed on the second conductivity type semiconductorlayer, wherein the light emitting structure comprises a mesa etchingregion where the second conductivity type semiconductor layer, theactive layer, and the first conductivity type semiconductor layer areetched, thereby exposing a portion of the first conductivity typesemiconductor layer in the mesa etching region, and the first electrodeis disposed on the exposed portion of the first conductivity typesemiconductor layer in the mesa etching region, wherein a firstelectrode layer is disposed between the second conductivity typesemiconductor layer and the second electrode, and a plurality of secondelectrode layer units is disposed between portions of the firstelectrode layer spaced from each other at opposite sides of the mesaetching region, and wherein opposite ends of the second electrode layerare disposed directly on the first electrode layer.
 2. The lightemitting device according to claim 1, wherein each of the firstelectrode layer and the second electrode layer is a transparentelectrode layer.
 3. The light emitting device according to claim 1,wherein the second electrode layer units are gradually increased innumber in a direction from a pad portion of the second electrode to anend portion of the second electrode.
 4. The light emitting deviceaccording to claim 1, wherein adjacent ones of the second electrodelayer units have a non-uniform spacing.
 5. The light emitting deviceaccording to claim 4, wherein the spacing between the second electrodelayer units is gradually reduced in a direction from a pad portion ofthe second electrode to an end portion of the second electrode.
 6. Thelight emitting device according to claim 1, wherein the second electrodelayer units have non-uniform widths, respectively.
 7. The light emittingdevice according to claim 6, wherein the widths of the second electrodelayer units are gradually increased in a direction from a pad portion ofthe second electrode to an end portion of the second electrode.
 8. Thelight emitting device according to claim 1, wherein an insulating layeris disposed between the mesa etching region and the second electrodelayer units.
 9. The light emitting device according to claim 8, whereinthe insulating layer is disposed inside a portion of the light emittingstructure exposed through the mesa etching region.